Automatic gain control (AGC) amplifiers generally have a non-linear gain response with respect to changes in the control voltage. In some applications, such as receivers associated with null steering antennas in satellite communications systems for example, it is desirable to have an AGC amplifier that provides linear gain in dB over a wide dynamic range.
One advantage of a linear AGC amplifier in a satellite tracking antenna system is that a portion of the electronic circuitry for a steering antenna can be effectively integrated into the amplifier itself, thus eliminating extra circuitry and/or software. More importantly, by knowing the linear slope of the amplifier's power curve, jamming can be more easily detected, quantified and corrected for. This aspect of a linear amplifier can be advantageous where a tracking antenna is located near a communications antenna operating at a close frequency. In this environment, the tracking antenna must be able to maintain satellite tracking in the presence of "friendly jamming" from high power communications transmissions.
Presently available AGC amplifiers do not combine a high signal level capability with a high gain response that is linear in dB as a result of linear changes in the control voltage. In addition, power dissipation is a major concern when high gain amplifiers are fabricated as monolithic integrated circuits. Thus, there is a need for an AGC amplifier implemented as a monolithic integrated circuit that also has high power handling capability, stable gain adjustable over a wide range, and linear gain response in dB with respect to changes in the control voltage.